Memory block erasure

ABSTRACT

Embodiments of memory block erasure are described herein. An aspect includes determining a first word line set consisting of a first plurality of word lines. Another aspect includes activating the first plurality of word lines, such that a respective memory cell that is connected to each of the first plurality of word lines is erased by the activation of the first plurality of word lines. Another aspect includes determining a second word line set, wherein the second word line set consists of the first word line set and a second plurality of word lines. Another aspect includes simultaneously activating the first plurality of word lines and the second plurality of word lines, such that a respective memory cell that is connected to each of the second plurality of word lines is erased by the activation of the first plurality of word lines and the second plurality of word lines.

BACKGROUND

The present techniques relate to computer memory. More specifically, thetechniques relate to the erasure of memory blocks in computer memory.

Computer memory may be organized in a hierarchy, from processorregisters, over multiple cache levels, to external main memory. Thehighest or uppermost cache level is the one closest to the processor,and the lowest cache level is the one closest to the main memory. Accesslatency is lowest, and bandwidth is highest, for registers and uppercache levels. For example, a data word in core static random accessmemory (SRAM) may be accessed in 1 clock cycle. For the cache, accessinga data word may require two to tens of cycles, and for the main memory,up to hundreds of cycles.

On a memory level, the memory is partitioned into arrays, which make uprandom access memory (RAM) cores. The RAM cores are designed to have arelatively small physical area. The cores are combined into a memoryarray. Memory arrays are gathered together into units, and thenconnected into cache memory by multiplexers. At the array level, data isorganized in words, with each word having a respective address. Each bitof each word is stored in a single cell. An SRAM cell may include 6transistors, including two cross-coupled inverters (including 4transistors) and two access transistors (or word line transistors).Write data is transmitted to the cells by bit lines. Read data istransmitted from the cell to the read-out circuit using either one ofthe two bit lines or using both bit lines. The number of cells on a bitline can be as any appropriate number, for example, from 16 to 1024cells per bit line.

SUMMARY

According to an embodiment described herein, a system can include logicto determine a memory block comprising a plurality of memory cells to beerased. The logic can also, based on determining the memory block,perform an erasure. The logic can also determine a first word line setconsisting of a first plurality of word lines, each of the firstplurality of word lines being connected to a respective memory cell ofthe plurality of memory cells. The logic can also activate the firstplurality of word lines corresponding to the first word line set, suchthat a respective memory cell that is connected to each of the firstplurality of word lines is erased by the activation of the firstplurality of word lines. The logic can also determine a second word lineset, wherein the second word line set consists of the first word lineset and a second plurality of word lines, each of the second pluralityof word lines being connected to a respective memory cell of theplurality of memory cells. The logic can also simultaneously activatethe first plurality of word lines and the second plurality of word linescorresponding to the second word line set, such that a respective memorycell that is connected to each of the second plurality of word lines iserased by the activation of the first plurality of word lines and thesecond plurality of word lines.

According to another embodiment described herein, a method can includedetermining a memory block comprising a plurality of memory cells to beerased. The method can also include, based on determining the memoryblock, performing an erasure. The method can also include determining afirst word line set consisting of a first plurality of word lines, eachof the first plurality of word lines being connected to a respectivememory cell of the plurality of memory cells. The method can alsoinclude activating the first plurality of word lines corresponding tothe first word line set, such that a respective memory cell that isconnected to each of the first plurality of word lines is erased by theactivation of the first plurality of word lines. The method can alsoinclude determining a second word line set, wherein the second word lineset consists of the first word line set and a second plurality of wordlines, each of the second plurality of word lines being connected to arespective memory cell of the plurality of memory cells. The method canalso include simultaneously activating the first plurality of word linesand the second plurality of word lines corresponding to the second wordline set, such that a respective memory cell that is connected to eachof the second plurality of word lines is erased by the activation of thefirst plurality of word lines and the second plurality of word lines.

According to another embodiment described herein, an apparatus can beconfigured to determine a memory block comprising a plurality of memorycells to be erased. The apparatus can also be configured to, based ondetermining the memory block, perform an erasure. The apparatus can alsobe configured to determine a first word line set consisting of a firstplurality of word lines, each of the first plurality of word lines beingconnected to a respective memory cell of the plurality of memory cells.The apparatus can also be configured to activate the first plurality ofword lines corresponding to the first word line set, such that arespective memory cell that is connected to each of the first pluralityof word lines is erased by the activation of the first plurality of wordlines. The apparatus can also be configured to determine a second wordline set, wherein the second word line set consists of the first wordline set and a second plurality of word lines, each of the secondplurality of word lines being connected to a respective memory cell ofthe plurality of memory cells. The apparatus can also be configured tosimultaneously activate the first plurality of word lines and the secondplurality of word lines corresponding to the second word line set, suchthat a respective memory cell that is connected to each of the secondplurality of word lines is erased by the activation of the firstplurality of word lines and the second plurality of word lines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example computer system that mayimplement memory block erasure;

FIG. 2 is a block diagram of an example static random access memory(SRAM) that may implement memory block erasure;

FIG. 3 is a process flow diagram of an example method for memory blockerasure;

FIG. 4 is an example chart illustrating an embodiment of memory blockerasure;

FIG. 5 is an example chart illustrating an embodiment of memory blockerasure; and

FIG. 6 is a block diagram of an example system for memory block erasure.

DETAILED DESCRIPTION

Embodiments of memory block erasure are provided, with exemplaryembodiments being discussed below in detail. Memory block erasure, e.g.,clearing of relatively large blocks of memory so that each cell in theblock of memory holds the same value (e.g., all cells hold ‘0’, or allcells hold ‘1’) after the erasure is completed, may be performedrelatively frequently in a computer system, and may affect overallsystem performance. Memory block erasure may be performed on a cacheline by cache line basis. However, for such an erasure, the complexityincreases linearly with the number of cache lines to be cleared becausethe address bits may activate a single word line at a time, requiringmany processor cycles to perform the erasure.

Memory cells may show a relatively large hysteresis due to contentionduring changing of that state of a memory cell. When a cell with content‘1’ is cleared (e.g., flipped to hold a content of ‘0’), the transistorsin the cell may fight against the clearing. A higher electrical currentbeing provided by the data-in drivers to the cell may reduce the timerequired to clear the cell, so that less total energy will be necessaryto clear or write the cell. In order to reduce hysteresis, a divide andconquer approach may be used over multiple iterations to erase a memoryblock. Initially, one or only a few cells on the bit line are erased.These cleared cells are activated in the next clearing step, and willhelp to erase other adjacent cells by increasing the driver strength ofthe data-in driver. In each subsequent iteration, there are more cellsthat have been erased, and the erased cells are activated along with thecells that are currently being cleared in order to reduce hysteresis. Insome embodiments, in each iteration, the number of activated cells maydouble, e.g., follow a binary power series. In some embodiments, after asingle initial word line is cleared in a first iteration, multiple wordlines are activated simultaneously during each subsequent iteration ofthe erasure. All of the cells in the memory block that is being erasedwill hold the same value after an erasure is completed. In someembodiments, all of the cells in the memory block may hold a value of‘0’ after the erasure; in other embodiments, all of the cells in thememory block may hold a value of ‘1’ after the erasure.

The cells that are selected for erasure may be distributed on the bitline in some embodiments, so that cells that have not yet been erasedmay have a relatively large distance to each other along the bit line,and are located near erased cells. The resistance between the cells maybe effectively reduced by distributing the activated cells along the bitline in some embodiments.

Turning now to FIG. 1, a computer system 100 is generally shown inaccordance with an embodiment. The computer system 100 can be anelectronic, computer framework comprising and/or employing any numberand combination of computing devices and networks utilizing variouscommunication technologies, as described herein. The computer system 100can be easily scalable, extensible, and modular, with the ability tochange to different services or reconfigure some features independentlyof others. The computer system 100 may be, for example, a server,desktop computer, laptop computer, tablet computer, or smartphone. Insome examples, computer system 100 may be a cloud computing node.Computer system 100 may be described in the general context of computersystem executable instructions, such as program modules, being executedby a computer system. Generally, program modules may include routines,programs, objects, components, logic, data structures, and so on thatperform particular tasks or implement particular abstract data types.Computer system 100 may be practiced in distributed cloud computingenvironments where tasks are performed by remote processing devices thatare linked through a communications network. In a distributed cloudcomputing environment, program modules may be located in both local andremote computer system storage media including memory storage devices.

As shown in FIG. 1, the computer system 100 has one or more centralprocessing units (CPU(s)) 101 a, 101 b, 101 c, etc. (collectively orgenerically referred to as processor(s) 101). The processors 101 can bea single-core processor, multi-core processor, computing cluster, or anynumber of other configurations. The processors 101, also referred to asprocessing circuits, are coupled via a system bus 102 to a system memory103 and various other components. The system memory 103 can include aread only memory (ROM) 104 and a random access memory (RAM) 105. The ROM104 is coupled to the system bus 102 and may include a basicinput/output system (BIOS), which controls certain basic functions ofthe computer system 100. The RAM is read-write memory coupled to thesystem bus 102 for use by the processors 101. The system memory 103provides temporary memory space for operations of said instructionsduring operation. The system memory 103 can include random access memory(RAM), read only memory, flash memory, or any other suitable memorysystems.

The computer system 100 comprises an input/output (I/O) adapter 106 anda communications adapter 107 coupled to the system bus 102. The I/Oadapter 106 may be a small computer system interface (SCSI) adapter thatcommunicates with a hard disk 108 and/or any other similar component.The I/O adapter 106 and the hard disk 108 are collectively referred toherein as a mass storage 110.

Software 111 for execution on the computer system 100 may be stored inthe mass storage 110. The mass storage 110 is an example of a tangiblestorage medium readable by the processors 101, where the software 111 isstored as instructions for execution by the processors 101 to cause thecomputer system 100 to operate, such as is described herein below withrespect to the various Figures. Examples of computer program product andthe execution of such instruction is discussed herein in more detail.The communications adapter 107 interconnects the system bus 102 with anetwork 112, which may be an outside network, enabling the computersystem 100 to communicate with other such systems. In one embodiment, aportion of the system memory 103 and the mass storage 110 collectivelystore an operating system, which may be any appropriate operatingsystem, such as the z/OS or AIX operating system from IBM Corporation,to coordinate the functions of the various components shown in FIG. 1.

Additional input/output devices are shown as connected to the system bus102 via a display adapter 115 and an interface adapter 116. In oneembodiment, the adapters 106, 107, 115, and 116 may be connected to oneor more I/O buses that are connected to the system bus 102 via anintermediate bus bridge (not shown). A display 119 (e.g., a screen or adisplay monitor) is connected to the system bus 102 by a display adapter115, which may include a graphics controller to improve the performanceof graphics intensive applications and a video controller. A keyboard121, a mouse 122, a speaker 123, etc. can be interconnected to thesystem bus 102 via the interface adapter 116, which may include, forexample, a Super I/O chip integrating multiple device adapters into asingle integrated circuit. Suitable I/O buses for connecting peripheraldevices such as hard disk controllers, network adapters, and graphicsadapters typically include common protocols, such as the PeripheralComponent Interconnect (PCI). Thus, as configured in FIG. 1, thecomputer system 100 includes processing capability in the form of theprocessors 101, and, storage capability including the system memory 103and the mass storage 110, input means such as the keyboard 121 and themouse 122, and output capability including the speaker 123 and thedisplay 119.

In some embodiments, the communications adapter 107 can transmit datausing any suitable interface or protocol, such as the internet smallcomputer system interface, among others. The network 112 may be acellular network, a radio network, a wide area network (WAN), a localarea network (LAN), or the Internet, among others. An external computingdevice may connect to the computing system 100 through the network 112.In some examples, an external computing device may be an externalwebserver or a cloud computing node.

It is to be understood that the block diagram of FIG. 1 is not intendedto indicate that the computer system 100 is to include all of thecomponents shown in FIG. 1. Rather, the computer system 100 can includeany appropriate fewer or additional components not illustrated in FIG. 1(e.g., additional memory components, embedded controllers, modules,additional network interfaces, etc.). Further, the embodiments describedherein with respect to computer system 100 may be implemented with anyappropriate logic, wherein the logic, as referred to herein, can includeany suitable hardware (e.g., a processor, an embedded controller, or anapplication specific integrated circuit, among others), software (e.g.,an application, among others), firmware, or any suitable combination ofhardware, software, and firmware, in various embodiments.

FIG. 2 is a block diagram of example bit line 200 of static randomaccess memory (SRAM) that may implement memory block erasure. The bitline 200 of FIG. 2 may comprise, for example, any of the memory in acomputer system such as computer system 100, such as RAM 105, and/orcache memory in CPUs 101 a-c. A computer memory may be made up of aplurality of bit lines such as bit line 200. A data input 201 isprovided to write transistors 202. Write transistors control writeaccess to all of the cells 204A-Z in the bit line 200. When the gates ofthe write transistors 202 are activated, the value on the data input 201is transmitted to the complementary bit line 203A and the true bit line203B. The bit line 200 as shown includes a plurality of cells 204A-Z; abit line 200 such as is shown in FIG. 2 may include any appropriatenumber of cells in various embodiments. Each of the cells 204A-Z isconnected across the complementary bit line 203A and the true bit line203B. As shown in FIG. 2, a cell 204A includes two word line transistors205 and 207, and cross-coupled inverter 206, which may hold a value of‘0’ or ‘1’. Each of the data cells 204A-Z includes respective word linetransistors and a cross-coupled inverter. The word line transistors 205and 207 are used to activate the individual cells in the bit line forreads and writes; each cell 204 A-Z has a respective word line that isaddressed by a word line decoder that is connected to the bit line 200.

During a read operation, one or both of the word line transistors 205and 207 may be activated, or opened, to connect a cell such as cell 204Ato bit line 203A and/or 203B. The data stored in cross-coupled inverter206 will pull the connected bit line to the positive or negative supplyrail voltage depending on the content (i.e., ‘0’ or ‘1) that is storedin the cross-coupled inverter 206. During a write operation in a cellsuch as cell 204A, both word line transistors 205 and 207 are activated.The cell pulls the connected bit lines 203A-B to the positive or to thenegative supply rail voltage. The array write transistors 202 connectthe bit lines 203A-B with the data input 201. If the write data on datainput 201 is of opposite polarity to the data held in the cross-coupledinverter 206 of the cell 204A, a short circuit current may flow acrossthe cell 204A for a relatively short amount of time in order to flip thecontents of the cell. This short-circuit condition is called contention.To reduce contention, in some embodiments, the data input driver voltageis made large enough to overwrite the cell voltage quickly. Reducedcontention may lead to power savings, enable a shorter cycle time, andreduce aging effects on the transistors and the surrounding metal layersin the memory that includes bit line 200.

It is to be understood that the block diagram of FIG. 2 is not intendedto indicate that the bit line 200 is to include all of the componentsshown in FIG. 2. Rather, the bit line 200 can include any appropriatefewer or additional components not illustrated in FIG. 2 (e.g.,additional transistors, inverters, lines, cells, counters, a drivertree, a word decoder, etc.). Further, the embodiments described hereinwith respect to bit line 200 may be implemented with any appropriatelogic, wherein the logic, as referred to herein, can include anysuitable hardware (e.g., a processor, an embedded controller, or anapplication specific integrated circuit, among others), software (e.g.,an application, among others), firmware, or any suitable combination ofhardware, software, and firmware, in various embodiments.

FIG. 3 is a process flow diagram of an example method for memory blockerasure. The method 300 can be implemented within any suitable computingdevice, such as the computer system 100 of FIG. 1, and is discussed withrespect to FIG. 2. In block 301, a bit line 200 of memory that is partof a block of memory to be erased is identified. The block of memorythat is being erased may include multiple bit lines; method 300 may beimplemented across one or more bit lines in various embodiments. Invarious embodiments, a subset of the cells in the identified bit line200 may be erased; in other embodiments, all of the cells in theidentified bit line 200 may be erased. In the identified bit line 200, avalue of 0 is provided on the data input 201, the write transistors 202are activated, and the read precharge is turned off. Next, in block 302,a counter N is initialized to 0. The counter N may be any appropriateimplementation of a counter. In block 303, word line set 0 is activatedbased on the value of counter N and the identified cells that are beingerased. Word line set 0 may be a single word line corresponding to asingle cell in some embodiments and may be word line 0 in someembodiments. In other embodiments, the single word line in word line set0 is selected to be in the middle of the bit line (e.g., word line 511for a bit line having 1024 cells), or may be the last cell in the bitline (e.g., word line 1023 for a bit line having 1024 cells) in furtherembodiments. In further embodiments in which a subset of the cells onthe bit line 200 are being erased, word line set 0 may include the firstcell in the subset of cells, a cell that is located in the middle of thesubset of cells, or the last cell in the subset of cells. When the wordline for the cell corresponding to word line set 0 is activated, theerasure data value on the data input 201 is written into thecross-coupled inverter 206 in the activated cell. In some embodiments,the erasure data value may be ‘0’, such that all erased cells in thememory block will hold a value of ‘0’; in other embodiments, the erasuredata value may be ‘1’, such that all erased cells in the memory blockwill hold a value of ‘1’. Counter N is then incremented in block 304.Next, in block 305, word line set 1, based on the value of counter N isactivated. Word line set 1 includes word line set 0, plus one or moreadditional word lines. The word lines in word line set 1 are activatedsimultaneously; the word line from word line set 0 may remain on duringthe entire erase procedure. The word lines in word line set 1 may beword lines 0 and 1 in some embodiments. In other embodiments, the wordlines in word line set 1 may be distributed across the bit line, e.g.,selected such that they two word lines in word line set 1 have a maximumdistance from one another. For example, word line set 1 may include wordlines 511 and 1023 for an erasure of all the cells on a bit line having1024 cells.

Flow then proceeds to block 306, in which it is determined whether theblock erase is complete. For example, if 2{circumflex over ( )}N isequal to the number of word lines in the block that is being erased, theblock erase may be determined to be complete in block 306. If it isdetermined in block 306 that the block erase is not complete, flowproceeds to block 307, in which counter N is incremented. From block307, flow returns to block 305, in which word line set N is activated.Word line set N includes all of the word lines that were included inword line set N−1, plus additional word lines. The word lines in wordline set N−1 may stay activated through subsequent iterations of blocks305-307. The word lines in word line set N are activated simultaneously.In some embodiments, the additional word lines in word line set N mayinclude word lines 2{circumflex over ( )}N−1 to 2{circumflex over ( )}N.In other embodiments, the additional word lines in word line set N maybe distributed across the bit line, e.g., selected such that the openedword lines have a maximum distance from one another. For example, theword lines in word line set N may be given by X*2{circumflex over( )}(Q−N)−1, for all integer values of X from 1 to 2{circumflex over( )}N, where the number of cells on a bit line that are erased in thewhole erasure sequence is 2{circumflex over ( )}Q. Blocks 305, 306, and307 are repeated until it is determined in block 306 that the blockerase is complete. When it is determined in block 306 that the blockerase is complete, flow proceeds to from block 306 to block 308, andmethod 300 ends. All of the cells on the bit line 200 that are part ofthe designated memory block may hold a value of 0 at the end of method300 in some embodiments. In other embodiments, all of the cells on thebit line 200 that are part of the designated memory block may hold avalue of 1 at the end of method 300.

The process flow diagram of FIG. 3 is not intended to indicate that theoperations of the method 300 are to be executed in any particular order,or that all of the operations of the method 300 are to be included inevery case. Additionally, the method 300 can include any suitable numberof additional operations.

FIG. 4 is an example chart 400 illustrating an embodiment of memoryblock erasure. The chart illustrates an embodiment of method 300 of FIG.3, and lists the specific word lines that are included in each word lineset for an example memory block erasure of 16 cells (e.g., word lines 0to 15) that are located on a single bit line. In the example of FIG. 4,the number of additional word lines in each word line set are selectedaccording to a binary power series, and are not distributed on the bitline. In this example, the number of word lines to be erased is 16;however, this is for illustrative purposes only. Any appropriate numberof cells on a bit line may be erased according to the embodimentillustrated by FIG. 4. Block 401A shows that word line set 0, which isactivated in block 303 of FIG. 3, consists of word line 0. The wordlines that have been activated may stay activated as method 300progresses, and additional word lines are activated in each iteration ofblock 305, 306, and 307 corresponding to each word line set as thecounter N is incremented. As shown in block 401B, word line set 1consists of word lines 0 and 1. Block 401C shows word line set 2consisting of 4 word lines (0, 1, 2 and 3). Block 401D shows word lineset 3 consisting of 8 word lines (0, 1, 2, 3, 4, 5, 6, and 7). Block401E shows word line set 4 consisting of 16 word lines (0, 1, 2, 3, 4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15). When 2{circumflex over ( )}Nis equal to the number of cells to be erased (in this example, whenN=4), the erase is complete for the particular bit line.

For an erasure of a larger number of cells according to the example ofFIG. 4, the counter N may continue to be incremented, and additionalword lines added to word line set N and activated, until the all of thedesignated cells are erased. For a word line set N, as shown in block401N, word lines 0 to 2{circumflex over ( )}N−1 are included. When2{circumflex over ( )}N is equal to the number of lines on the bit linethat are being erased as part of the designated memory block, the eraseis complete for the particular bit line.

FIG. 5 is an example chart 500 illustrating another embodiment of memoryblock erasure. The chart illustrates an embodiment of method 300 of FIG.3, and lists the specific word lines that are included in each word lineset for an example memory block erasure of 16 cells (e.g., word lines 0to 15) on a single bit line. In the example of FIG. 5, the number ofadditional word lines in each word line set are selected according to abinary power series, and are distributed on the bit line. In thisexample, the number of cells to be erased is 16; however, this is forillustrative purposes only. Any appropriate number of cells on a bitline may be erased according to the embodiment illustrated by FIG. 5.Block 501A shows that word line set 0, which is activated in block 303of FIG. 3, consists of word line 15, which is selected due to being thelast cell in the set of 16 cells that are being erased. The word linesthat have been activated stay activated as method 300 progresses, andadditional word lines are activated in each iteration of block 305, 306,and 307 corresponding to each word line set as the counter N isincremented. As shown in block 501B, word line set 1 consists of wordlines 7 and 15; word line 7 is selected as being located in halfwaybetween the erased word line 15 and the bit line drivers. Block 501Cshows word line set 2 consisting of 4 word lines (3, 7, 11, and 15).Block 501D shows word line set 3 consisting of 8 word lines (1, 3, 5, 7,9, 11, 13, and 15). Block 501E shows word line set 4 consisting of 16word lines (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15).When 2{circumflex over ( )}N is equal to the number of cells to beerased (in this example, when N=4), the erase is complete for theparticular bit line.

For an erasure of a larger number of cells on a single bit lineaccording to the example of FIG. 5, the initial word line set 0 may beselected to be at the end of the cells that are being erased, andadditional word lines may be added to subsequent word line sets based ontheir distance from the already-erased word lines. For example, for abit line that includes 1024 cells that are all being erased, word lineset 0 may be word line 1023 in some embodiments. As counter N isincremented, a word line set N, as shown in block 501N, may include wordlines X*2{circumflex over ( )}(Q−N)−1, for all integer values of X from1 to 2{circumflex over ( )}N, wherein 2{circumflex over ( )}Q is thenumber of cells on the bit line that is being erased. When N is equal toQ, the erase is complete.

In some embodiments, the cells on a bit line may have a relatively largemismatch due to inconsistencies in the manufacturing process. Therefore,for a relatively large value of N with many word lines being activatedsimultaneously, the mismatch may be badly distributed, e.g., the cellshaving a content of ‘0’ may be weaker cells and the cells having acontent of ‘1’ may be stronger cells. In such embodiments, the number ofadditional word lines in each subsequent word line set may be lower thanthe value given by the binary power series (as discussed above withrespect to FIGS. 4 and 5). In some embodiments, the number of additionalword lines may be constant for a number of subsequent word line sets,based on a detected amount of mismatch along the bit line. The number ofadditional word lines in each word line set may be any appropriatenumber (e.g., 4), and may vary across word line sets, in variousembodiments.

FIG. 6 is a block diagram of an example system 600 for memory blockerasure. System 600 may implement method 300 of FIG. 3, and may beincluded in any appropriate memory, such as RAM 105 and/or cache memoryin CPUs 101 a-c, of FIG. 1, and may be implemented in conjunction withone or more bit lines 200 as shown in FIG. 2. System 600 includes acounter 601 that outputs a counter signal 602. In some embodiments, thecounter 601 may be a finite state machine comprising a thermometercounter. In such an embodiment, the counter signal 602 from counter 601may be a a plurality of outputs a0 to aN, and the counter 601 may, wheninitialized, output 1 on output a0, and output 0 on outputs a1 to aN.Each time the counter 601 is incremented, an additional output ofoutputs a0 to aN is given a value of 1, starting at output a1 andproceeding in order to output aN. Therefore, when the counter value N isequal to 1, outputs a0 and a1 have a value of 1, and all other outputshave a value of 0. In such an embodiment, the counter outputs 602 a0 toaN of the counter 601 are provided to a driver tree 603. The thermometerimplementation of counter 601 is discussed for illustrative purposesonly; any appropriate counter implementation may be used in conjunctionwith various embodiments of system 600 for memory block erasure.

The driver tree 603 determines word line sets to activate for the memoryblock erasure based on the counter signal 602 from counter 601, anddistributes erase signals on erase signal outputs 604A-Z to the wordlines in the current word line set via a plurality of OR gates 605A-Z.In various embodiments, the driver tree 603 may determine the word linesets for which the erase signals are activated in any appropriatemanner, such as described above with respect to FIGS. 3, 4, and 5. Eachof the OR gates 605A-Z is associated with a single respective word lineWL0 to WLZ, and each word line addresses a respective cell, such ascells 204A-Z of FIG. 2. Each of the OR gates 605A-Z receives an inputfrom word decoder 606, which addresses cells in the memory for reads andwrites during normal operation of the memory, and an input from arespective erase signal of erase signal outputs 604A-Z from the drivertree 603. Each OR gate 605A-Z activates the OR gate's respective wordline via the OR gate's word line output WL1-WLZ based on the state ofthe two inputs. As the counter 601 is incremented from 0 to Nmax, where2{circumflex over ( )}Nmax is the number of cells being erased in theblock erase, the word line set that is determined by driver tree 603grows until all of the cells in the memory block that is being erased(which may be some or all of the cells 204A-Z) have received an erasesignal on an erase signal output 604A-Z from driver tree 603. When noblock erase is being performed, the erase signal outputs 604A-Z from thedriver tree 603 are zero, and the word decoder 606 operates to selectthe connected cells for reads and writes via the OR gates 605A-Z. Thedriver tree 603 may also determine, based on the value of the counter601, whether the memory block erasure is complete, e.g., when2{circumflex over ( )}N, where N is the current value of the counter601, is equal to the number of cells being erased.

It is to be understood that the block diagram of FIG. 6 is not intendedto indicate that the system 600 is to include all of the componentsshown in FIG. 6. Rather, the system 600 can include any appropriatefewer or additional components not illustrated in FIG. 6 (e.g., logicgates, lines, etc.). Further, the embodiments described herein withrespect to system 600 may be implemented with any appropriate logic,wherein the logic, as referred to herein, can include any suitablehardware (e.g., a processor, an embedded controller, or an applicationspecific integrated circuit, among others), software (e.g., anapplication, among others), firmware, or any suitable combination ofhardware, software, and firmware, in various embodiments.

The present techniques may be a system, a method or an apparatus. Theflowchart and block diagrams in the Figures illustrate the architecture,functionality, and operation of possible implementations of systems,methods, and apparatus according to various embodiments of the presenttechniques. In this regard, each block in the flowchart or blockdiagrams may represent a module, segment, or portion of logic forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The descriptions of the various embodiments of the present techniqueshave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A system, comprising logic to: determine a memoryblock comprising a plurality of memory cells to be erased; and based ondetermining the memory block, perform an erasure comprising: determininga first word line set consisting of a first plurality of word lines,each of the first plurality of word lines being connected to arespective memory cell of the plurality of memory cells; activating thefirst plurality of word lines corresponding to the first word line set,such that a respective memory cell that is connected to each of thefirst plurality of word lines is erased by the activation of the firstplurality of word lines; determining a second word line set, wherein thesecond word line set consists of the first word line set and a secondplurality of word lines, each of the second plurality of word linesbeing connected to a respective memory cell of the plurality of memorycells; and simultaneously activating the first plurality of word linesand the second plurality of word lines corresponding to the second wordline set, such that a respective memory cell that is connected to eachof the second plurality of word lines is erased by the activation of thefirst plurality of word lines and the second plurality of word lines. 2.The system of claim 1, wherein the logic is to: determine an initialword line set, the initial word line set consisting of a single wordline; and activate the single word line corresponding to the initialword line set, such that a first memory cell that is connected to thesingle word line is erased by the activation of the single word line;and wherein the first plurality of word lines consists of the singleword line and one additional word line.
 3. The system of claim 2,wherein the one additional word line corresponds to a second memory cellhaving a maximum distance from the first memory cell along a bit linethat includes the first memory cell and the second memory cell.
 4. Thesystem of claim 3, wherein the second plurality of word lines isselected such that the first plurality of word lines and the secondplurality of word lines are evenly distributed along the bit line. 5.The system of claim 1, wherein a number of the second plurality of wordlines is equal to a number of the first plurality of word lines, andwherein the second plurality of word lines is distinct from the firstplurality of word lines.
 6. The system of claim 1, wherein the logic isto: initialize a value N of a counter based on the determining theplurality of memory cells to be erased; increment the value N of thecounter based on activating a word line set; determine a subsequent wordline set based on a value of the counter, wherein a number of word linesin the subsequent word line set is equal to 2{circumflex over ( )}N; andbased 2{circumflex over ( )}N being equal to a number of the pluralityof memory cells, determine that the erasure is complete.
 7. The systemof claim 6, wherein the logic is to: provide the value N of the counterto a driver tree that determines the subsequent word line set, whereinthe driver tree provides erase signals to memory cells corresponding tothe subsequent word line set via inputs of a plurality of OR gates, eachof the plurality of OR gates having an output that is connected to arespective memory cell, and wherein each of the plurality of OR gatesreceives an input from a word decoder.
 8. The system of claim 6, whereineach of the plurality of memory cells holds a value of ‘1’ after theerasure is complete.
 9. A computer-implemented method, comprising:determining a memory block comprising a plurality of memory cells to beerased; and based on determining the memory block, performing an erasurecomprising: determining a first word line set consisting of a firstplurality of word lines, each of the first plurality of word lines beingconnected to a respective memory cell of the plurality of memory cells;activating the first plurality of word lines corresponding to the firstword line set, such that a respective memory cell that is connected toeach of the first plurality of word lines is erased by the activation ofthe first plurality of word lines; determining a second word line set,wherein the second word line set consists of the first word line set anda second plurality of word lines, each of the second plurality of wordlines being connected to a respective memory cell of the plurality ofmemory cells; and simultaneously activating the first plurality of wordlines and the second plurality of word lines corresponding to the secondword line set, such that a respective memory cell that is connected toeach of the second plurality of word lines is erased by the activationof the first plurality of word lines and the second plurality of wordlines.
 10. The computer-implemented method of claim 9, comprising:determining an initial word line set, the initial word line setconsisting of a single word line; and activating the single word linecorresponding to the initial word line set, such that a first memorycell that is connected to the single word line is erased by theactivation of the single word line; and wherein the first plurality ofword lines consists of the single word line and one additional wordline.
 11. The computer-implemented method of claim 10, wherein the oneadditional word line corresponds to a second memory cell having amaximum distance from the first memory cell along a bit line thatincludes the first memory cell and the second memory cell.
 12. Thecomputer-implemented method of claim 11, wherein the second plurality ofword lines is selected such that the first plurality of word lines andthe second plurality of word lines are evenly distributed along the bitline.
 13. The computer-implemented method of claim 9, wherein a numberof the second plurality of word lines is equal to a number of the firstplurality of word lines, and wherein the second plurality of word linesis distinct from the first plurality of word lines.
 14. Thecomputer-implemented method of claim 9, comprising: initializing a valueN of a counter based on the determining the plurality of memory cells tobe erased; incrementing the value N of the counter based on activating aword line set; determining a subsequent word line set based on a valueof the counter, wherein a number of word lines in the subsequent wordline set is equal to 2{circumflex over ( )}N; and based 2{circumflexover ( )}N being equal to a number of the plurality of memory cells,determining that the erasure is complete.
 15. An apparatus configuredto: determine a memory block comprising a plurality of memory cells tobe erased; and based on determining the memory block, perform an erasurecomprising: determining a first word line set consisting of a firstplurality of word lines, each of the first plurality of word lines beingconnected to a respective memory cell of the plurality of memory cells;activating the first plurality of word lines corresponding to the firstword line set, such that a respective memory cell that is connected toeach of the first plurality of word lines is erased by the activation ofthe first plurality of word lines; determining a second word line set,wherein the second word line set consists of the first word line set anda second plurality of word lines, each of the second plurality of wordlines being connected to a respective memory cell of the plurality ofmemory cells; and simultaneously activating the first plurality of wordlines and the second plurality of word lines corresponding to the secondword line set, such that a respective memory cell that is connected toeach of the second plurality of word lines is erased by the activationof the first plurality of word lines and the second plurality of wordlines.
 16. The apparatus of claim 15, configured to: determine aninitial word line set, the initial word line set consisting of a singleword line; and activate the single word line corresponding to theinitial word line set, such that a first memory cell that is connectedto the single word line is erased by the activation of the single wordline; and wherein the first plurality of word lines consists of thesingle word line and one additional word line.
 17. The apparatus ofclaim 16, wherein the one additional word line corresponds to a secondmemory cell having a maximum distance from the first memory cell along abit line that includes the first memory cell and the second memory cell.18. The apparatus of claim 17, wherein the second plurality of wordlines is selected such that the first plurality of word lines and thesecond plurality of word lines are evenly distributed along the bitline.
 19. The apparatus of claim 15, wherein a number of the secondplurality of word lines is equal to a number of the first plurality ofword lines, and wherein the second plurality of word lines is distinctfrom the first plurality of word lines.
 20. The apparatus of claim 15,configured to: initialize a value N of a counter based on thedetermining the plurality of memory cells to be erased; increment thevalue N of the counter based on activating a word line set; determine asubsequent word line set based on a value of the counter, wherein anumber of word lines in the subsequent word line set is equal to2{circumflex over ( )}N; and based 2{circumflex over ( )}N being equalto a number of the plurality of memory cells, determine that the erasureis complete.